1. FIELD OF THE INVENTION
This invention pertains to the field of wheel hubs and axles for motor vehicles. More particularly, the invention pertains to wheel bearings and lubricant seals used in combination with axles and wheel hubs.
2. DESCRIPTION OF THE PRIOR ART
Unitized seals, such as those used with a wheel bearing of a motor vehicle, generally include an outer sleeve, held by a slight interference on a first element, and an inner sleeve, also held by slight interference fit on a second element, the first and second elements supported for mutual relative rotation. The outer surface of the outer sleeve and the inner surface of the inner sleeve are generally covered with elastomeric material, which produces hydraulic sealing contact due to the interference fit on the first and second elements, respectively.
In order to provide a hydraulic seal that prevents movement of fluid, usually axle lubricant, through the seal between the inner and outer sleeves, a sealing lip formed of elastomer is forced resiliently by a garter spring into sealing contact with a surface of the inner sleeve. In addition, various sealing lips are formed integrally with the elastomer and held by the inherent elasticity of the elastomer in contact with the inner seal or outer seal. These lips prevent movement of contaminants through the seal and help preserve integrity of the axle lubricant.
A unitized seal of the this type includes also a bumper pad molded integrally with the elastomer and is supported rotatably on either the inner or outer sleeve. The bumper pad is generally located at a slight clearance from an inner surface of the other sleeve than the sleeve to which it is fixed.
Ideally upon installation of a unitized seal in the axle assembly, the bumper pad remains spaced from the sleeve, thereby preventing inward migration of contaminants entrained in the axle lubricant. The size of the clearance between the bumper pad and adjacent sleeve surface determines the size of contaminants that are filtered and excluded from entering the seal.
However, it has been discovered that as the sleeve is installed, frequently the clearance between the bumper pad and the adjacent sleeve surface is closed entirely and that the bumper pad is held instead in resilient contact with the sleeve contrary to its intended spacial relationship. Furthermore, the bumper pad and sleeve are in frictional contact with a force applied to the contact surface whose magnitude can be substantial depending on the conditions of assembly. As a result of this, it has been observed that relatively high in service temperatures are produced in the sleeve due to the preloaded contact and relative rotation between the bumper pad and sleeve.